Search for Axionlike Particles Produced in e+e- Collisions at Belle II

Abstract

We present a search for the direct production of a light pseudoscalar a decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process e+e-??a, a??? in the mass range 0.2<ma<9.7 GeV/c2 using data corresponding to an integrated luminosity of (445�3) pb-1. Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axionlike particles or ALPs) are frequently postulated in extensions of the standard model. We find no evidence for ALPs and set 95% confidence level upper limits on the coupling strength ga?? of ALPs to photons at the level of 10-3 GeV-1. The limits are the most restrictive to date for 0.2<ma<1 GeV/c2. � 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.